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Landsat satellites captured a pair of images showing changes in the glacier and lake during the last 26 years. Landsat 5 acquired this image on Aug. 22, 1987. Snow and ice appear white, and forests are green. The brown streaks on the glaciers are lateral and medial moraines.

Located in the Brabazon Range of southeastern Alaska, Yakutat Glacier is one of the fastest-retreating glaciers in the world. It is the primary outlet for the 810-square-kilometer (310-square-mile) Yakutat Ice Field, which drains into Harlequin Lake and, ultimately, the Gulf of Alaska. Comparing satellite images from 1987 and 2013 show how quickly Yakutat is melting away.

What is causing the rapid retreat? University of Alaska glaciologist Martin Truffer and colleagues pointed to a number of factors in their 2013 study published in the Journal of Glaciology. The chief cause is the long-term contraction of the Yakutat Ice Field, which has been shrinking since the height of the Little Ice Age.

Landsat 8 captured this image on Aug. 13, 2013. During the last 26 years, the glacier’s terminus has retreated more than 5 kilometers (3 miles).

Once part of a much larger ice field, Yakutat has been contracting for hundreds of years. As other nearby glaciers retreated, Yakutat Ice Field was cut off from higher-elevation areas that once supplied a steady flow of ice from the north. With that flow cut off, there simply isn’t enough snow falling over the low-elevation Yakutat Ice Field to prevent it from retreating.

Beyond this natural change, human-caused global warming has hastened the speed of the retreat. Between 1948–2000, mean annual temperatures in Yakutat increased by 1.38° Celsius (2.48° Fahrenheit). Between 2000 and 2010, they rose by another 0.48°C (0.86°F). The warmer temperatures encourage melting and sublimation at all ice surfaces exposed to the air.